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1.
William J. Reed 《Natural Resource Modeling》1989,3(4):463-480
It is assumed that the probability of destruction of a biological asset by natural hazards can be reduced through investment in protection. Specifically a model, in which the hazard rate depends on both the age of the asset and the accumulated invested protection capital, is assumed. The protection capital depreciates through time and its effectiveness in reducing the hazard rate is subject to diminishing returns. It is shown how the investment schedule to maximize the expected net present value of the asset can be determined using the methods of deterministic optimal control, with the survival probability regarded as a state variable. The optimal investment pattern involves “bang-bang-singular” control. A numerical scheme for determining jointly the optimal investment policy and the optimal harvest (or replacement) age is outlined and a numerical example involving forest fire protection is given. 相似文献
2.
林先治 《南京林业大学学报(自然科学版)》1996,20(3):95-98
以生产实践资料为依据,对福建省贮木场林用装卸桥基本参数进行分析探讨,以使贮木场林用装卸桥设计的基本参数更加科学合理,达到减少造价、降低成本、保证质量、提高效率、增进效益的目的 相似文献
3.
Soil classification systems are widely used for quickly and easily summarizing soil properties and provide a shorthand method of communication between scientists, engineers, and end-users. Two of the most widely used soil classification systems are the United States Department of Agriculture (USDA) textural soil classification system and the Unified Soil Classification System (USCS). Unfortunately, not all soil map units are classified according to the USDA or USCS systems, and previous attempts to provide a crosswalk table have been inconsistent. Random Forest machine learning model was used to create a USCS prediction model using USDA soil property variables. Important variables for predicting USCS code from available soil properties were USDA soil textures, percent organic material, and available water storage. Prediction error rates less than 2% were achieved compared to error rates of approximately 40% using crosswalk methods. 相似文献
4.
百里杜鹃林马缨杜鹃种群结构和动态研究 总被引:7,自引:0,他引:7
百里杜鹃林是贵州西北部特有的自然景观和植物群落,马缨杜鹃是该群落的主要建群种,本文在种群的水平上从马缨杜鹃在不同生境中的大小级,密度、年龄结构和分布格局进行分析研究,探讨它们的动态规律和演变趋势,进而探索整个百里杜鹃林的发展演变趋势,为这一特殊自然景观的保护和利用提出一定的理论依据和建设决策参考数据。 相似文献
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6.
多光谱成像技术诊断植物病虫害的人工神经网络模型 总被引:4,自引:0,他引:4
为了实现可靠的植物病虫害诊断,提出把人工神经网络和多光谱成像技术结合的方法,并将该方法用于常见的三种黄瓜病害的识别研究。在此基础上,实验采用窄带多光谱成像技术获取患病黄瓜叶面的14个可见光通道和近红外通道、全色通道的多光谱图像。利用BP网络对病斑样本的光谱信息进行学习分类。和14通道训练结果比较,增加850nm的近红外通道和全色通道,使网络的训练时间缩短、预测能力提高。实验结果表明,这种方法对植物进行快速、准确和非破坏性诊断提供可靠的技术支持。 相似文献
7.
This paper examines the effects of timber harvesting by skidding on some soil properties (sand, silt, clay, pH, organic carbon, bulk density and compaction), herbaceous cover (unit mass) and forest floor (unit weight) properties. Also N (%), P, K, Na, Ca, Mg, Fe, Zn, Cu and Mn (ppm) were determined in all herbaceous cover, forest floor and two soil depth (0–5 cm and 5–10 cm) on skidroad of an oak (Quercus petrea L.) stand in Istanbul Belgrad Forest – Turkey. In this study, obtained results are; the forest floor and the herbaceous cover amount on the skidroad have been found considerably lower than undisturbed area. There were some crucial changes in the characteristics of the soil which has been investigated down to 10 cm depth. Soil bulk density was found quite high in the samples taken from the skidroad subject to compaction compared to the ones on the undisturbed area. Nevertheless, no important difference had been detected between the skidroad and the undisturbed area at both soil depths in terms of organic carbon contents. Moreover, the soil acidity (pH) values showed noteworthy differences in the analysis of soil samples taken from both soil depths on the skidroad and on the undisturbed area. Fe and Cu contents of herbaceous samples on skidroad were significantly higher than undisturbed area. Forest floor on skidroad had significantly higher K content, and significantly lower Zn, Mn and N content compared to undisturbed area. P, Fe, Zn and Mn contents were found significantly lower in 0–5 cm soil depth on skidroad than undisturbed area. In 5–10 cm soil depth, concentrations of N, P, Fe, Zn and Mn were significantly lower, while Mg and Cu contents were significantly higher than undisturbed area. Results indicate that long-term harvest using skidding techniques on these sites had adversely affected soil cation concentrations, physical soil conditions and mass of herbaceous cover and forest floor. 相似文献
8.
9.
讨论森林病虫害的离散模型.根据森林病虫害传播的特征,针对各分块区域之间已感病树不互相转移的情况,建立差分方程模型;讨论系统的平衡点,并对无病平衡点和地方病平衡点进行稳定性分析,得到地方病平衡点稳定的充分条件;用Matlab进行多种情况的数值模拟,验证了理论结果. 相似文献
10.